Draw contours on an unstructured triangular grid.
tricontour() and
tricontourf() draw contour lines and
filled contours, respectively. Except as noted, function
signatures and return values are the same for both versions.

If a string, like ‘r’ or ‘red’, all levels will be plotted in this
color.

If a tuple of matplotlib color args (string, float, rgb, etc),
different levels will be plotted in different colors in the order
specified.

alpha: float
The alpha blending value

cmap: [ None | Colormap ]
A cm Colormap instance or
None. If cmap is None and colors is None, a
default Colormap is used.

norm: [ None | Normalize ]
A matplotlib.colors.Normalize instance for
scaling data values to colors. If norm is None and
colors is None, the default linear scaling is used.

levels [level0, level1, …, leveln]
A list of floating point numbers indicating the level
curves to draw, in increasing order; e.g., to draw just
the zero contour pass levels=[0]

origin: [ None | ‘upper’ | ‘lower’ | ‘image’ ]
If None, the first value of Z will correspond to the
lower left corner, location (0,0). If ‘image’, the rc
value for image.origin will be used.

This keyword is not active if X and Y are specified in
the call to contour.

extent: [ None | (x0,x1,y0,y1) ]

If origin is not None, then extent is interpreted as
in matplotlib.pyplot.imshow(): it gives the outer
pixel boundaries. In this case, the position of Z[0,0]
is the center of the pixel, not a corner. If origin is
None, then (x0, y0) is the position of Z[0,0], and
(x1, y1) is the position of Z[-1,-1].

This keyword is not active if X and Y are specified in
the call to contour.

locator: [ None | ticker.Locator subclass ]
If locator is None, the default
MaxNLocator is used. The
locator is used to determine the contour levels if they
are not given explicitly via the V argument.

extend: [ ‘neither’ | ‘both’ | ‘min’ | ‘max’ ]
Unless this is ‘neither’, contour levels are automatically
added to one or both ends of the range so that all data
are included. These added ranges are then mapped to the
special colormap values which default to the ends of the
colormap range, but can be set via
matplotlib.colors.Colormap.set_under() and
matplotlib.colors.Colormap.set_over() methods.